General

• Guild of American Luthiers
• American String Teacher's Association
• Catgut Acoustical Society
• American Society of Ancient Instruments

Violin

• Violin Making
• International Violin Competition of Indianapolis
• Do you have a Stradivarius label? If you've found one in your violin go look at this site!
• International Violinmakers school of Cremona
• The Violin Society of America

Viola

• American Viola Society
• Viola Society Website

Cello

• Internet Cello Society
• UNC Greensboro Cello Collection includes scanned scores held in UNCG's Special Collections.
  

Bass

• International Society of Bassists
• Contrabass.com

Guitar

• Classical Guitar Home Page
• Stropes.com - Finger-Style Guitar Music Publishing & Education
• Home page for Luthiers or guitar builders
• Stewart-MacDonald: Everything for building and repairing stringed instruments!
• Guitar Foundation of America
• Harpguitars.net Home Page
• Jazz Guitar ONLINE

UWM Music Library's String Pedagogy web resources

• http://www.uwm.edu/~rlittman/stringped.html